Insulated electrical conductor



De@ 11, 1934 l B. H. REEvEs 1,983,564

INSULATED ELECTRI CAL CONDUCTOR Filed Deo. 16, 1932 /yo//aw (are ATTORNEYS Patented Dee. 11, 1934 UNITED STATES PATENT OFFICE INSULATED ELECTRICAL CONDUCTOR Application December 1s, 1932, serial No. 647,533

6 Claims.

This invention relates to insulated electrical conductors and has for its object the provision of an improvedv article of this character. 'I'he invention is especially directed to the provision of an improved electric cable for low voltage power networks, and contemplates for such purposes a cable having ellective inherent arc-quenching characteristics upon the occurrence of a short circuit or similar fault.

In my copending applications for Letters Patent of the United States, Serial No. 550,063, illed Julyll, 1931 and Serial No.606,617,n1ed April 21.

1932. I have disclosed an insulated -electrical conductor in which eective arc-extinguishing characteristics are obtained by associating with the insulation surrounding the conductor a compound (such as urea) which when heated, by the occurrence of a short-circuit or similar iault, evolves `a considerable volume of arc-quenching gases. I have now found that a considerable proportion, i! not all, of the arc-quenching compound may be advantageously placed within the hollow core of the various types of hollow core cables or conductors. Similarly, a name-resisting material may be advantageously placed in the core of such conductors. Arc-quenching compounds are usually llame resistant, although the reverse is not always true.

The present invention thus comprises an insulated electrical conductor having a core containing an arc-extinguishing compound or a llameresistant substance or both. Several types of hollow core cables or conductors are now on the market and the invention contemplates illling, to an appropriate extent, the hollow core of such a cable or conductor with an' arc-extinguishing and/or flame-resisting compound. Where the compound is liquid at atmospheric temperatures it is most conveniently included in the hollow core in the i'orm of an absorbent medium impregnated with the compound. Solid compounds'may be packed in the hollow core in any appropriate manner.- The insulation surrounding the metallic conductor may itself contain arc-quenching and/or llame-resisting substances, so that upon the occurrence of a short-circuit or similar fault arc-quenching and/or llame resisting gases will be evolved in eilective volume from both within and without the metallic conductor.

In the accompanying drawing Fig. 1 shows an insulated hollow core cable embodying the invention, with its various concentric layers exposed for illustration, and

Figs. 2 to 13 show various types of core construction for hollow core cables or conductors.

(Cl. T13- 264) The hollow core oi the cable shown nFig. 1 is a formed tube of copper or the like. The metallic conductor element, usually in stranded form, surrounds the hollow core. The metallic conductor is surrounded by an insulating layer of relatively 5 high dielectric strength, such as a felted Wall 0I asbestos impregnated with a compound consisting of about 40% chlorined phenol and 60% gilsonite. 'Ihe first insulating layer is surrounded by an arc-quenching insulating layer, such as another wall of felted asbestos impregnated with urea or other appropriate arc-quenching compound. The second insulating layer is covered with a tightly woven braid of asbestos yarn, which in turn is covered with the usual lead sheath to form the 15 completed cable. This and other suitable forms of arc-quenching'insulation surrounding the metallic conductor are described in my aforementioncdA patent applications.

In accordance with the present invention the hollow core of the cable contains an arc-quenching and/or flame-resisting compound. A convenient method ofinserting the arc-quenching or flame-resisting substance within the hollow core is to saturate strands or ropes of ilbrous material with a solution of the compound in an appropriate solvent thereof. Upon removal of the solvent, in the course of manufacture of the cable, the compound remains in the librous material. Asbestos is admirably adapted to serve as the carrier for the arc-extinguishing compound because of its non-inilammability and also because it will not generate any inammable or explosive gas at elevated temperatures.

Any appropriate arc-quenching or llame-resisting compound may be placed in the hollow core, such, for example, as urea, chlorinated phenols (or diphenol) antimony chloride, ammonium chloride, ammonium bromide, ammonium phosphate, chlorinated naphthalene etc. Where the compound is liquid at atmospheric and temperatures normally attained in the use of the cable, it should preferably be carried in the hollow core by a suitable absorbent medium, such as a strand or rope of asbestos or other suitable brous material. Even Awhen solid at ordinary temperatures, I prefer to melt or dissolve the compound and impregnate an absorbent or porous medium therewith, as the means of inserting and retaining the compound in the hollow core. Compounds which are solid at ordinary temperatures may, on the other hand, be inserted and retained in the core in various other ways.

Upon the occurrence of a short-circuit or other fault developing a sumciently high tem- 55 perature to damage the metallic conductor, effective volumes of arc-quenching or dame-resisting gases such as ammonia will be evolved by the compound in the hollow core of the cable. The volume of gases thus evolved maybe adequate to quench any arc or ame, but in any case will supplement similar gases evolved from the insulationsurrounding the conductor, thereby requiring less external arc-quenching insulation. Thus, by the invention, the central cavity of hollow core cables is put to protable and advantageous use and the amount of external arcquenching insulation which would otherwise be required is reduced.

The invention may be embodied in any type of hollow core cable. The aim in the hollow core cable is toconcentrate the vmetallic conductor in that part of the cross-section of the finished cable where it will carry the most current. In order to accomplish this aim various means are used to produce a hollow core around which the copper or other metallic wires are stranded or cabled. In Figs. 2 to 6 of the drawing, I have illustrated certain types of core construction in which the present invention may be advantageously cmbodied.

Figs. 2, 3 and 4 illustrate a coil spring type of hollow core construction, which may bemade up of round copper wire, helically wound with close turns to produce a hollow core, or with :flat or rectangular strip material wound inthe same manner.

In Figs. 5 and 6 the hollow core is in the form of a twisted I-beam of copper or the like. The metallic rod, of I-beam section, is twisted (lightning rod fashion) so as to provide a substantially circular form against which the wires of the metallic conductor are cabled. The cavity on each side of the I-beam is lled w'ith an arcquenching and/or name-resisting compound in accordance with the present invention.

The hollow lcore illustrated in Flgs. 7 and 8 is made from a dat strip of copper rolled around to form a tube as it goes into the cabling machine.

The hollow core shown in Figs. 9 and 10 is made 'of copper`A strips having'a ship-lap edge placed in longitudinal engagement with a slight spiral lay to provide flexibility.

'Ihe core illustrated in Figs. 11 and 12 consists of a rope of I'lbrous material, such as a manila rope or an asbestos rope. In this case the fibrous rope, constituting the core of the cable, is utilized as the carrier for the arc-extinguishing or flameresisting compound.

The invention may of course be embodied in other types of hollow core construction. In any case, the advantages of the invention are attained by appropriately incorporating an arc-extinguishing and/or flame-resisting substance in the cavity of a hollow core cable or conductor, as for example by placing the substance directly in the cavity or by putting in a ibrous ller saturated or impregnated with the substance.

I claim: I

1. An insulated electrical conductor having a hollow core substantially lled with a fibrous material impregnated with an arc-extinguishing compound.

2. A hollow core electric cable having a brous filler in the cavity ofthe hbllow core thereof, .and an arc-extinguishing compound associatedwith said brous ller.

3. An insulated electrical conductor having a hollow core containing asbestos impregnated withv an arc-extinguishing compound.

4. An insulated electrical conductor having.a hollow core containing one or more flame-resist` ing and arc-eitinguishing substances selectedfrom the group consisting of urea, chlorinated phenols, chlorinated diphenols, chlorinated naph-V thalene, ammonium halides, and ammonium'- phosphate. v

5. An insulated electric cable having a hollow- 

